Retaining walls and freestanding walls are used in various landscaping projects and are available in a wide variety of styles. Numerous methods and materials exist for the construction of retaining walls. Such methods include the use of natural stone, poured concrete, precast panels, masonry, and landscape timbers or railroad ties.
In recent years, segmental concrete retaining wall units, which are dry stacked (i.e., built without the use of mortar), have become widely accepted in the construction of retaining walls. An example of such a unit is described in U.S. Pat. No. Re 34,314 (Forsberg). Such retaining wall units have gained popularity because they are mass produced and, consequently, relatively inexpensive. They are structurally sound, easy and relatively inexpensive to install, and couple the durability of concrete with the attractiveness of various architectural finishes. The retaining wall system described in U.S. Pat. No. Re 34,314 (Forsberg) has been particularly successful because of its use of a block design that includes, among other design elements, a unique pinning system that interlocks and aligns the retaining wall units, thereby providing structural strength and allowing efficient installation. This system is advantageous in the construction of larger walls, when combined with the use of geogrids hooked over the pins, as described in U.S. Pat. No. 4,914,876 (Forsberg). However, in smaller walls, for example, walls of three foot height or less this connection system of interlocking pins is unnecessary for wall stability and adds to the cost of the system and complexity of wall construction.
Another important feature of retaining wall blocks and blocks used in free standing walls is the appearance of the block. The look of weathered natural stone is very appealing for walls. There are several methods in the art to produce concrete wall blocks having an appearance that to varying degrees mimics the look of natural stone. One well known method is to split the block during the manufacturing process so that the front face of the block has a fractured concrete surface that looks like a natural split rock. This is done by forming a slab in a mold and providing one or more grooves in the slab to function as one or more splitting planes. The slab is then split apart to form two or more blocks. Another method is wherein blocks are individually formed in a mold and the surfaces are textured by removal of the mold. Additional machine texturing processes can then be applied. Many manufacturers also vary the color and the texture or pattern on the front face of the block. It might be desirable for the face of the block to be smooth, serrated, or grooved or to have an aggregate appearance.
Another method to create a weathered stone appearance is to tumble the blocks together with other blocks in a large rotating canister. The collisions of the blocks in the tumbler chips off random pieces of the blocks, rounding the edges and creating a look that can be quite close to the appearance of a natural stone. This is a labor intensive undertaking that also can result in undesirable damage to the blocks and high overall costs of production.
Many manufacturers also vary the color and the texture or pattern on the front face of the block. It might be desirable for the face of the block to be smooth, serrated, or grooved or to have an aggregate appearance.
Creating a random, or ashlar, pattern in the face of a wall is highly desirable. This gives the appearance of a mortared or dry-stacked natural stone wall, which is a traditional and well accepted look. Some current wall blocks are intended to create an ashlar pattern. However, the creation of a truly random appearance requires the production of multiple block shapes for use in a single retaining wall. This is inefficient from a production standpoint because this requires multiple molds and more kinds of blocks to inventory. If only one face of the block is intended to be the front face, then the block system will suffer a trade-off between having enough face sizes to create a random, natural appearance and the cost and inefficiency of using multiple molds and creating multiple inventory items.
The shape of the block is also an important feature during installation of a retaining wall. Forsberg '876 illustrates a fairly complex shape for a retaining wall block which is particularly advantageous in the construction of curved walls. The block is symmetrical about a vertical plane which bisects the block at a midway point through the front and back faces.
Many commercially available blocks are symmetrical about a plane bisecting the front and back surfaces. Typically such blocks have planes rather than axes of symmetry, as there are differences between the top and bottom surfaces of such blocks. Clearly, blocks that are substantially square or rectangular (i.e., each surface being joined to another at an orthogonal angle) exhibit a great deal of symmetry. Other blocks are more complex in shape and exhibit only one vertical plane of symmetry. For example, U.S. Pat. No. 5,711,130 (Shatley) illustrates a block having substantially parallel front and back faces and non-parallel, mirror-image side wall surfaces. That is, there is a mirror plane of symmetry that vertically bisects the block. U.S. Pat. No. 5,598,679 (Orton et al.) and U.S. Pat. No. 5,294,216 (Sievert) illustrate a type of block having parallel front and back faces and non-parallel, converging side surfaces. The term “converging side surfaces” means that the side walls of the blocks converge as they approach the rear of the block. Such blocks are also symmetrical about a vertical plane that passes through the front and back surfaces.
There are advantages to having non-parallel surfaces on these blocks when constructing a retaining wall. The angles formed by these side surfaces permits construction of curvilinear walls, and moreover, permit the amount of curvature to vary according to the terrain and desired appearance of the wall.
However, problems still remain in the field of retaining walls and free standing walls. Easy-to-use methods and systems that result in safe, stable and cost effective walls are continually sought.
It would be desirable to have a system of blocks for constructing a wall that combines the ability to improve the reinforcement of the wall with the ease of installation of modern segmental walls, while still providing for an attractive appearance of a natural stone wall. The block system should allow the construction of retaining walls, freestanding walls, straight walls, and curved walls.